The present invention concerns a packaging sheet intended for packaging a cheese product, the packaging sheet comprising:
an internal membrane, comprising at least one internal plastic layer intended to be oriented towards the cheese product and at least a first water-absorbing layer made of a first water-absorbing material;
a printable external surface, the external surface being intended to be oriented away from the cheese product.
FR 2 716 174 discloses a packaging sheet for packaging cheese products, which comprises:
an internal membrane formed of a layer of paper, which is coated with paraffin on its internal surface, i.e. on its surface intended to be oriented towards the packaged cheese product; and
an external membrane, intended to be oriented towards the exterior of the package, i.e. away from the cheese product and made of a plastic material mixed with a water absorbing substance. The external plastic membrane is microperforated.
However, such a packaging sheet is not entirely satisfactory. Indeed, there is a direct contact between the packaged cheese product and the paraffin of the internal membrane, whose role is to prevent molds, and in particular the penicillium and/or geotricium, present on the cheese product, from growing on the paper of the internal membrane. Use of paraffin in the food packaging industry is being more and more frowned upon due to potential health issues stemming from its use. Therefore, it is desirable to avoid the presence of paraffin when developing packaging.
Moreover, extending the conservation time of cheese is a concern for cheese manufacturer. The packaging sheet of FR 2 716 174 is not entirely satisfactory in this regard, because the water and air flow through the packaging from the cheese product to the atmosphere is insufficiently controlled.
One of the purposes of the present invention is to provide a packaging sheet which is adapted for extending the conservation time of cheese, especially Camembert type soft cheese, while at the same time avoiding the use of paraffin.
To this end, according to a first aspect of the invention, the or each internal plastic layer has a plurality of microperforations arranged in a random fashion on the or each internal plastic layer in such a manner that the air permeability of the internal membrane is comprised between 5 mL/min Bendtsen and 500 mL/min Bendtsen, the first water-absorbing material having a water absorption rate comprised between 1 and 30 g/m2 as measured using the COBB test C3600.
The random distribution of the microperforations results, where wanted, in a very uniform permeability and allows for a good control of the air and water exchanges through the packaging sheet.
The Applicant has found that a key aspect for extending the conservation time of the cheese is promptly removing the liquid water under the form of microdroplets located on the outer surface of the cheese product, on the cheese flora. The air permeability range and the water absorption range mentioned above are well suited for that purpose. The air permeability is representative of the number of microperforations and of the total surface area of the microperforations. Said parameters are important to ensure that the liquid water located on the cheese flora will pass through the internal layer and reach the water-absorbing layer. The water absorption rate is important to make sure that water is properly kept away from the cheese product surface.
The ranges above allow for a sufficient evacuation of the water in liquid and vapor state without drying out the cheese. The first water-absorbing layer retains the water transferred from the cheese product through the microperforations of the internal membrane. It acts as a buffer and prevents the dehydration of the cheese product. The presence of the first water-absorbing layer allows for an improved control of the rate of flow through the packaging sheet.
The microperforations comprise through-holes extending through the or each internal plastic layer and blind-holes which open out on the internal surface of the innermost internal plastic layer.
A preferred range for the air permeability of the internal membrane is comprised between 5 mL/min Bendtsen and 500 mL/min Bendtsen, particularly between 10 mL/min Bendtsen and 200 mL/min Bendtsen, between 10 mL/min Bendtsen and 50 mL/min Bendtsen or even between 10 mL/min Bendtsen and 30 mL/min Bendtsen. A preferred range for the water absorption rate of the first water-absorbing material is comprised between 1 and 30 g/m2 as measured using the COBB test C3600, particularly between 3 and 25 g/m2 as measured using the COBB test C3600, and between 10 and 22 g/m2 as measured using the COBB test C3600. Any air permeability range can be combined with any water absorption range. A particularly preferred combination is an air permeability range between 10 mL/min Bendtsen and 50 mL/min Bendtsen, with a water absorption range between 2 and 22 g/m2 as measured using the COBB test C3600 and even 10 to 30 ml/min Bendtsen combined with 10 to 22 g/m2 as measured using the COBB test C3600. Said combination is well suited for the maturation of soft cheese with white rind, such as Camembert or Brie.
The air permeability is measured using the method disclosed in the international standard ISO 5636-3. It is for example measured using the air permeance tester sold by the company Lorentzen & Wettre used in Bendtsen measure mode.
Although in the present specification, the air permeability ranges are expressed in mL/min Bendtsen and measured using the Bendtsen method, any other air permeability unit and corresponding method can be used for measuring the air permeability. In this case, the claimed and disclosed ranges should be converted from mL/min Bendtsen into these other units.
The water-absorption rate is measured using the COBB test C3600, which is well known in the art. The procedural standards used are the same as those explained in TAPPI T441 except for the duration of the test, which lasts one hour (C3600) instead of 60 seconds (C60) as described in TAPPI T441.
Other features of the packaging sheet according to the invention will be described hereafter.
The density of microperforations on an internal surface of the internal plastic layer is comprised between 500 and 5000 microperforations per dm2, preferably comprised between 1000 and 4000 microperforations per dm2, and even more preferably between 1600 and 3000 microperforations per dm2.
Said densities are average values, on at least 50% of the surface area of the packaging sheet.
The density range is well suited for obtaining the required range for the air permeability of the internal membrane. It is adapted for extending the conservation time of a cheese product, especially a Camembert type soft cheese.
The first water-absorbing material is a cellulose-based material. The first water absorbing layer is for example made of paper, preferably of Kraft type paper.
Preferably, the first water-absorbing material has a surface weight (grammage) comprised between 20 and 70 g/m2, and in particular a grammage of 25 to 45 g, more particularly of 30 to 50 g, and for example 32 g.
Optionally, the packaging sheet further comprises a second water-absorbing layer made of a second water-absorbing material. The second water-absorbing layer is superimposed on the first water-absorbing layer. The second water-absorbing layer provides additional water storage capacity. It is particularly useful for packaging very wet cheeses. The second water-absorbing material is a cellulose-based material. The second water-absorbing layer is for example a cellulose film or a layer of paper, preferably of Kraft type paper. The second paper layer for example has a grammage of 20 to 40 g, and in particular a grammage comprised between 21 and 25 g.
The or each internal plastic layer preferably comprises one of a petroleum-based plastic material, a plastic material derived from renewable sources or a mixture of a petroleum-based plastic material and a plastic material derived from renewable sources.
Petroleum-based plastic materials are plastic materials that are derived from petroleum. The petroleum-based plastic material is for example chosen among: polyethylene (PE), in particular low density polyethylene, linear low density polyethylene or metallocene, polyamide (PA), polypropylene (PP), polyester, ethylene methyl acrylate (EMA), ethylene butyl acrylate (EBA), ethylene acrylic acid (EAA) or a ionomer and their blends, and other materials or resins that would be well known by those skilled in the art.
Plastic materials derived from renewable sources are plastic materials comprising carbons of renewable origin. These carbons are for example extracted from the biomass (e.g. from corn, wheat, soy or pine trees) or produced by microorganisms. The plastic materials derived from renewable sources are for example: polylactic acid (PLA), polyhydroxybutyrate (PHB) or their mixtures, polyhydroxyalkanoates (PHA) or blends of PLA with Mater-Bi® sold by the company Novamont, and other materials or resins that would be well known by those skilled in the art.
Plastic materials derived from renewable sources are more environment-friendly than petroleum-based plastic materials since they derive from renewable resources rather than fossil resources.
Optionally, the internal membrane comprises at least two superimposed internal plastic layers. In one embodiment, at least two of the internal plastic layers are made of different plastic materials. For example, the innermost internal plastic layer is made of a material that adheres poorly to the first water-absorbing layer and the outermost internal plastic layer is made of a plastic material that adheres well to the first water-absorbing layer. In this case, the outermost internal plastic layer promotes adhesion of the innermost internal plastic layer to the first water-absorbing layer. Providing different internal plastic layers made of different plastic material may also allow for adjusting the mechanical or chemical properties of the internal membrane depending on the different plastic materials used. In another embodiment, all the internal plastic layers are made of the same plastic material. Providing several superimposed internal plastic layers rather than one single internal plastic layer made in one piece also modifies the properties, e.g. the mechanical properties, of the internal membrane.
Optionally, the internal plastic layer may have areas having different densities of microperforations. This feature allows tailoring the flow of water and air in a given area of the packaging sheet to the area of the cheese product, it is intended to surround. It thus allows creating different functional areas on the packaging sheet. Different values of permeability are thus obtained in these different areas.
The greatest dimension of the microperforations of the internal plastic layer in the plane of the internal plastic layer is preferably comprised between 10 and 500 μm. Having microperforations with sizes in this range increases the duration of conservation of the packaged cheese product.
According to one embodiment, the packaging sheet further comprises an external layer which is at least partially bonded to the internal membrane, the external surface being formed by a surface of the external layer oriented away from the internal membrane. The external layer helps control the rate of desorption of the water from the first water-absorbing layer towards the environment.
The external layer is for example made of a plastic material.
The external plastic layer preferably comprises one of a petroleum-based plastic material, a plastic material derived from renewable sources or a mixture of a petroleum-based plastic material and a plastic material derived from renewable sources.
The petroleum-based plastic material is for example chosen among those cited above in respect of the internal plastic layer.
The plastic material derived from renewable sources is for example chosen among those cited above in respect of the internal plastic layer.
The external layer can made of an aluminum foil as well. Such external layer is well suited for packaging cheese with a low water content or which are sensitive to gas, particularly oxygen.
Alternatively, the external layer is a paper layer.
According to one embodiment, the external layer is perforated.
A first possibility is having the microperforations arranged in a random fashion. The microperforations are obtained in the same way as the microperforations of the internal plastic layer.
Alternatively, the external layer has microperforations arranged in a regular pattern. The external layer can be perforated for example using needles for example. In this case, the microperforations form a regular pattern, repeated over the external layer.
In both cases, the air permeability of the external layer is preferably comprised between 0.1 and 40000 mL/min Bendtsen, preferably between 10 to 10000 mL/min Bendtsen, even preferably between 500 and 5000 mL/min Bendtsen. This air permeability is in particular obtained through the presence of microperforations in the external layer. These microperforations allow for a good control of the diffusion of the water vapour through the external layer, which is desirable. Indeed, if the flow rate is too rapid, the first water-absorbing layer will dry out quickly and suck more humidity from the cheese resulting in a drying out of the packaged cheese. On the contrary, a flow rate that is too slow may result in a degradation of the cheese flora, the formation of condensation on the internal surface or a deterioration of the packaging sheet, and in particular of the paper layers that are possibly present.
According to one embodiment, the air permeability of the external layer is greater than the air permeability of the internal membrane. Such a permeability gradient increases the speed of desorption of the water from the water-absorbing layer. It is adequate for example for packaging sheets intended for packaging cheese products having a weight loss of about 3 to 8%, in particular of about 4 to 5%.
According to another embodiment, the air permeability of the external layer is smaller than the air permeability of the internal membrane. Such a permeability gradient reduces the flow of air and water through the external layer from the water-absorption layer to the environment. It is advantageous for cheese products having a weight loss during maturation smaller than 2.5%, more particularly smaller than 1.5%, or when it is desirable to promote the retention of the water in the water-absorbing layer, rather than its desorption from this layer.
According to one embodiment, the external layer is only partially bonded to the internal membrane, for example along a set of bonding points, lines and/or graphic symbols. Adequate adhesives are for example a hotmelt adhesive, a pressure-sensitive adhesive or a water-based adhesive, such as a dextrin or a casein based adhesive. The adhesive is transparent or colored. A partial bonding between the external layer and the internal membrane allows for the needed evacuation of the water vapour comprised in the internal membrane.
In another embodiment, the external layer is bonded to the internal membrane along its entire surface facing the internal membrane. Adequate adhesives are for example waxes, such as petroleum-based waxes or waxes derived from renewable sources, pressure sensitive adhesives, water-based adhesives or adhesives comprising polyurethane, polyester, or polyurethane or polyester derivates.
The external layer is bonded to the internal membrane directly or indirectly e.g. through the second water-absorbing layer.
In one embodiment, the external surface is formed on the internal membrane. According to one more particular embodiment, the packaging sheet is in the form of a single sheet. “Single sheet” means that the different layers are formed onto one another for example by extrusion of one layer onto another, rather than being formed separately and later adhered to one another. A packaging sheet in the “single-sheet” form is advantageous since its production cost is reduced compared to a “multisheet” packaging sheet.
According to one embodiment, the first water-absorbing layer is made of paper having a grammage between 30 and 40 g, the internal plastic layer being made of polyethylene having a surface weight between 10 and 12 g/m2, the air permeability of the internal membrane being comprised between 10 mL/min Bendtsen and 50 mL/min Bendtsen, preferably between 10 and 30 mL/min Bendtsen, the first water-absorbing material having a water absorption rate comprised between 10 and 22 g/m2 as measured using the COBB test C3600.
Preferably, the packaging sheet in this case comprises an external layer partially bonded to the internal membrane, made of oriented polypropylene, for example 20 μm thick.
The invention also relates to a packaging comprising the packaging sheet as described above and a cheese product, arranged in the packaging sheet in such a way that the internal plastic layer is oriented towards the cheese product.
Preferably, the cheese product is one of a soft cheese, a fresh cheese or a blue cheese, even though other types of cheese products can be packaged in the packaging sheet. The packaging sheet is particularly suited to packaging a soft cheese with a white rind, such as Camembert or Brie.
In one embodiment, the packaging sheet is folded around the food product. The packaging sheet is not sealed to itself in a gas tight fashion. In another embodiment, the packaging sheet is sealed to itself, typically along a weld line, in a gas tight fashion. It creates a gas tight chamber where the cheese product is received. The packaging sheet is for example a flow pack in this case.
The invention also relates to the use of a packaging sheet having the features above, for packaging a cheese product in order to slow the maturation of the cheese product, in such a way that the NPT/NT ratio is lower than 13 after 45 days of maturation, preferably lower than 12.5 after 45 days of maturation, NPT being the quantity of nitrogen soluble in phosphotungstic acid, NT being the total quantity of nitrogen, the ratio NPT/NP being assessed using the Kjeldhal method according to the amended standard NF ISO8968-1.